In hearing devices and optionally also in other hearing apparatuses, telephone coils are frequently provided, with which telephone signals can be inductively received and emitted. The inductive transmission is however comparatively susceptible to interference when additional electrical and/or magnetic components are located in the vicinity of the transmission path. In particular the electromagnetic earpiece of a hearing device has been found to interfere with the received or emitted signals of a telephone coil. It has furthermore been established that the battery contacts of a hearing device also act as jamming transmitters. Depending on their form and current flow they produce more or less strong magnetic fields and thereby reduce the signal-to-noise ratio in signal transmission using the telephone coil.
Until now this has been addressed by positioning a compensating coil in an appropriate manner in the hearing device such that the interference fields produced by the magnetic earpiece or battery contacts are compensated for as far as possible. One disadvantage of this compensation is that the compensating coils used are comparatively voluminous. In hearing devices in particular this is generally unacceptable, to such an extent that such compensating coils must frequently be dispensed with.
A hearing device is known from DE 198 09 567 C2, in which in order to suppress genetic interference fields a second induction coil is provided in parallel to a first induction coil. The induction voltages produced counteract each other due to the inverse circuit, and interference signals can be minimized as a result.
A hearing device is known from WO 03/001844 A1 in which the magnetic interference effect is diminished by means of a compensating coil and a capacitor connected in parallel to a battery.